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Read this article to learn about the role of xanthones as MAO inhibitors and CNS depressants.
1, 6-Dihydroxyxanthone and 1, 3, 6-trihydroxyxanthone exhibited much potent inhibitory activity toward rat brain mitochondrial MAO (type A). On the other hand, 1, 3, 7-trihydroxyxanthone showed great potency for inhibition of mouse liver mitochondrial MAO (type B).
These results indicate that 1, 3, 6-trihydroxyxanthone and 1, 3, 7-trihydroxyxanthone were rather specific inhibitors of type MAO-A and type MA010-B, respectively. 1,3-Dihydroxy-6-alkoxyxanthones containing alkoxy residues with carbon number 1 to 8 were synthesized and compared for their inhibitory activity toward rat brain mitochondrial MAO.
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Among them, 6-ethoxy-, 6-propyloxy-, and 6-butyloxy-derivatives were potent inhibitors, and especially, 1, 3-dihydroxy-6-propyloxyxanthone was the most inhibitory. The xanthone aglycone produces signs of dose dependent weak CNS stimulant activities. This effect may be due to MAO inhibition.
The inhibition of type A and type B MAO by number of xanthones has been reported. Bellidifolin and 1,3,5,8- tetra substituted xanthones has been shown to be selective inhibitor of type A MAO in vitro, but the glucosides (Bellidifolin-8-O glucoside and desmethylbellidifolin-8-Oglucoside) showed no activity.
The significant CNS depressant action has been shown by tetra oxygenated xanthones and their O-glucosides of Swertia chirata and S. purpurascens.
Vasorelaxant Activity:
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1, 5-Dihydroxy-2, 3-dimethoxy-xanthone (HM-5) is one of the naturally occurring xanthones of a Tibetan medicinal herb Halenia elliptica.
Recently, it has been shown that HM-5 is one of the phase I metabolites of 1-hydroxy-2, 3, 5-trimethoxy-xanthone (HM-1), the major active component of H. elliptica with potent vasorelaxant actions. (Wang et al., 2008). A series of xanthones and xanthonoxypropanolamines have been synthesized. The activity of compounds on cardiovascular system was evaluated.
All the compounds tested exhibited effective hypotensive activity in anesthetized rats.
An oxypropanolamine side chain substituted at the C-3 position of xanthone nucleus significantly enhanced the hypotensive activity. Xanthones and xanthone derivatives have been shown to have beneficial effects in some cardiovascular diseases, including ischemic heart disease, atherosclerosis, hypertension and thrombosis.
The protective effects of xanthones in the cardiovascular system may be due to their antioxidant, anti-inflammatory, platelet aggregation inhibitory, antithrombotic and/or vasorelaxant activities. In particular, the antagonism of endogenous nitric oxide synthase inhibitors by xanthones may represent the basis for improved endothelial function and for reduction of events associated with atherosclerosis.
